Edit Thumbnail Cropping in Media Library

If you only want the change to apply to the thumbnail select “Apply changes to thumbnail” in “Thumbnail Settings”

Click and drag the cursor over the image to highlight the area you want to use for the thumbnail. If the thumbnail is square you can adjust the dimensions in the “Image Crop” area to give equal width and height. You can also drag the selection around to get the position just perfect

Click the “Crop” option above the image

Click the “Save” button below the image to save your changes

Now if you go back into the “Edit Image” option you should see the new thumbnail